X402 Payment Header Shape: checks a caller-supplied payment header for bounded base64 or JSON shape using only bounded caller-supplied values. Call when you need a bounded x402 payment header shape result before paying for or accepting an x402 or agent delivery assembled from caller-supplied challenge and result metadata. Returns contract-specific checks, normalized evidence, mismatch reasons, and an explicit acceptance or rejection status for X402 Payment Header Shape as versioned deterministic JSON. Price: $0.001 USDC via x402 on Base or Solana. First-party, stateless, memory-only execution with no paid upstream, live RPC, web search, credentials, custody, signing, media generator, or input retention. Honest limit: Validates metadata only; it never settles payment, signs payloads, contacts a facilitator, refunds funds, or asserts on-chain truth. Advisory output only; the buyer owns authorization, payment policy, and production decisions.